The present invention relates to a reinforcing structure of a vehicle body, and in particular relates to the reinforcing structure of the vehicle body in which the vehicle body is reinforced by a band plate which is made from synthetic resin and into which a reinforcing material is incorporated.
Conventionally, it is known that a panel member, such as a floor panel, a bonnet (engine hood), a trunk lid, or a roof panel, tends to be easily deformed by a force inputted from a suspension or the like. Especially, since the floor panel which forms a bottom face of a cabin is provided with a tunnel portion which protrudes in the cabin and extends in a longitudinal direction at a central portion, in a vehicle width direction, of the floor panel, the rigidity of this floor panel is lower than that of a flat-plate structure without the tunnel portion, which causes an increase of a membrane (film) vibration that the floor panel is displaced vertically. This vibration increase of the floor panel causes a cabin noise, so that there is a concern that the riding comfortability may be deteriorated.
In these days, carbon fiber reinforced plastic (CFRP) has been widely used as a structural material of airplanes, vehicles or the like because it has the material property of having a high strength ratio (strength/specific gravity) and a high rigidity ratio (rigidity/specific gravity), that is, being light weighted and strong/stiff. Since this carbon fiber reinforced plastic is configured such that carbon fiber shares the aerodynamics property of strength and the like and base material resin (matrix) shares the stress transmission function between carbon fibers and the protection function of carbon, the carbon fiber reinforced plastic is an anisotropic material of having greatly different physical properties in direction of a fiber direction and an non-fiber direction (a load's burden direction). The present applicant has proposed technologies that the carbon fiber reinforced plastic is used as the reinforcing material of the vehicle body based on the above-described knowledge.
A panel structure for a vehicle of Japanese Patent Laid-Open publication No. 2015-174611 comprises a damping (attenuation) panel member which is connected to a side sill and a second floor frame at four corners thereof, wherein the damping panel member includes a panel-shaped synthetic-resin made viscoelastic member and a carbon fiber member which is embedded in the viscoelastic member, fixed at four corners of the damping panel member, has a higher rigidity than the viscoelastic member, and arranged in a longitudinal direction. Thereby, an undercover to insulate noise from the outside is constituted and also the membrane vibration which is generated at the undercover itself is damped (reduced). A vehicle-body reinforcing structure of Japanese Patent Laid-Open publication No. 2017-061170 is that respective both end portions, in a longitudinal direction, of plural band plates which are made from the carbon fiber reinforced plastic and into which carbon fibers are incorporated in a state of being arranged in a longitudinal direction are respectively connected to vehicle-body-side connection portions which are provided below a floor panel, being spaced apart from in a vehicle longitudinal direction and a vehicle width direction. Thereby, damping of the vibration generated at a whole part of the vehicle body is attained.
In general, the vibration energy inputted to the band plate made from the carbon fiber reinforced plastic is transferred to the strain energy and the kinetic energy, and this strain energy is temporarily stored inside a member as shearing strain. Then, the stored strain energy (shearing strain) is transferred to the kinetic energy again. Herein, part of the strain energy is transferred to the heat energy, which is dissipated. Therefore, by increasing the strain energy stored inside the band plate, the dissipated heat energy cab be increased, so that the vibration damping performance of the vehicle can be increased. FIG. 10 shows a partial enlarged view of the carbon fiber reinforced plastic in a state before a torsional moment is applied, and FIG. 11 shows a partial enlarged view of the carbon fiber reinforced plastic in a state after the torsional moment has been applied. As shown in FIGS. 10 and 11, according to the reinforcing structure of the above-described second patent document, when the torsional moment based on the vibration energy of the floor panel is applied to the band plate, carbon fibers C are twisted and deformed independently, so that a base material M which exists between the carbon fibers C has shearing deformation. However, since the amount of the base material M between the carbon fibers C is very small, the shearing strain occurs increasingly at the base material M between the carbon fibers C and the stain energy stored inside the base material M is increased accordingly.
A move mode of a vehicle body which influences the riding comfortability of a passenger is classified into the two basically. The first vehicle-body mode is a vehicle-body torsional mode. This vehicle-body torsional mode is a torsional displacement move of the vehicle body itself which is caused by a phase delay based on the torsional moment around a vehicle-body central axis generated during the vehicle cornering, which is the vehicle-body mode related to the rigidity. The second vehicle-body mode is a membrane vibration mode. This membrane vibration mode is a vertical displacement move of the floor panel which is generated when the vehicle rides on projections existing on a road surface or the vehicle travels on a rough road, which is the vehicle-body mode related to the vibration.
According to the vehicle-body reinforcing structure of the above-described second patent document, the vehicle-body torsional mode generated at the whole part of the vehicle body is suppressed by the band plate connecting a pair of right-and-left tunnel side frames in the vehicle width direction, and also the membrane vibration mode generated at the floor panel is suppressed by the band plate connecting the tunnel side frame and a floor frame in the vehicle width direction. However, since the carbon fiber reinforced plastic is the anisotropic material in which a torsional-loss coefficient is three times greater than a bending-loss coefficient, there is room for further improving the vibration damping performance (the strain-energy storing capacity) of the band plate of the vehicle-body reinforcing structure of the above-described second patent document.
Since the band plate connecting the tunnel side frame and the floor frame of the above-described second patent document is deformed in a substantially similar manner to the floor panel, the torsional deformation substantially similar to the floor panel and the out-of-plane deformation in a direction perpendicular to the band plate occur. Therefore, even if the carbon fiber reinforced plastic making the band plate has the high strain-energy storing capacity as physical properties of the material itself, in a case where the band plate performs the same deformation move as the floor panel (or the flame member connected to the floor panel), only the amount of strain energy which corresponds to the torsional deformation accompanying this move is stored inside the band plate, so that the vibration damping performance of the band plate may not be effectively utilized.